1. Field of the Invention
This invention generally relates to a manufacturing method of a light-emitting element, and in particular, relates to a manufacturing method of a light-emitting element including a process of removing a surface layer of a side face of the light-emitting element.
2. Description of the Related Art
A light-emitting element is a device emitting a light such as a LED (Light Emitting Diode) or a LD (Laser Diode). The light-emitting element is used in a light source for a display or in an illumination, in addition to an optical communication system and a memory device using an optical memory media. There is a demand for a light-emitting element that has high photoelectric conversion efficiency and is inexpensive.
Recently, there has been developed a light-emitting element in which a GaN (gallium nitride)-based light-emitting layer is formed on a hard substrate composed of such as sapphire or SiC (silicon carbide). There is a demand for cutting the hard substrate into a small chip-sized device productively in order to reduce a cost of manufacturing a light-emitting element. In a case of a GaN-based LED having a sapphire substrate, the chip size is 300 μm and the sapphire substrate is hard. Therefore, mass productivity is low with respect to a dicing method or scribe and break method using a diamond scriber that is ordinarily used as a separating method of light-emitting element. There is a method of dividing a sapphire substrate by irradiating a laser to the sapphire substrate.
Japanese Patent Application Publication No. 2004-165226 (hereinafter referred to as Document 1) discloses a method in which devices are divided into chips after a laser light is irradiated to a division region of the sapphire substrate and a melted and re-solidified region or an evaporating and re-solidified region in a recess formed on the sapphire substrate is subjected to a blast treatment.
FIG. 1A through FIG. 1C illustrate a problem of a conventional art. As shown in FIG. 1A, an n-type GaN cladding layer 12, a GaInN quantum well active layer 14 and a p-type GaN cladding layer 16 are formed on a sapphire substrate 10 as a light-emitting portion 30. An electrode 18 is formed on the n-type cladding layer 12. An electrode 19 is formed on the p-type cladding layer 16. A laser light is irradiated from a face of the sapphire substrate 10 opposite to the light-emitting portion 30 to a division region for separating a light-emitting element. As shown in FIG. 1B, a recess 20 is formed on the division region of the sapphire substrate 10 being irradiated with the laser light, because the sapphire evaporates.
As shown in FIG. 1C, the sapphire substrate 10 is divided along the recess 20, and a light-emitting element (LED) 32 is formed. The light-emitting element 32 emits a light in four directions from the light-emitting portion 30. The face of the sapphire substrate 10 opposite to the light-emitting portion 30 is referred to as a light-emitting face S1.
The inventor searched an emitted light quantity from a light-emitting element that is separated with the method shown in FIG. 1A through FIG. 1C and from a light-emitting element that is separated with a scribe and break method. The scribe and break method is a method in which breaking is performed after scribing without a laser irradiation. As a result, it is confirmed that the emitted light quantity from the light-emitting element separated with the method shown FIG. 1A through FIG. 1C is lower than that from the light-emitting element separated with the scribe and break method by approximately 10%.
A region, of which temperature is increased with the laser irradiation without evaporation, is altered in the division region to which the laser is irradiated, and an altered layer 22 is formed, according to an examination of the inventor. It is confirmed that the emitted light quantity is reduced because of a light absorption of the altered layer 22. And, it is confirmed that the altered layer 22 extends deeply in the sapphire substrate 10 as shown in FIG. 2 along the laser light even if the recess 20 is not deep, as shown in FIG. 1B. It is therefore not possible to remove the altered layer 22 extending deeply in the sapphire substrate 10 even if the method of Document 1 is used. And it is not possible to sufficiently restrain the reduction of the emitted light quantity caused by the altered layer 22, even if the method of Document 1 is used.